Estimating turbulent velocities in the elliptical galaxies NGC 5044 and NGC 5813

The interstellar and intra-cluster medium (ICM) in giant elliptical galaxies and clusters of galaxies is often assumed to be in hydrostatic equilibrium. Numerical simulations, however, show that about 5%-30% of the pressure in a cluster is provided by turbulence induced by, for example, the central active galactic nucleus and merger activity. The authors aim to put constraints on the turbulent velocities and the turbulent pressure in the ICM of the giant elliptical galaxies NGC 5044 and NGC 5813 using XMM-Newton reflection grating spectrometer (RGS) observations. The magnitude of the turbulence is estimated using the Fe XVII lines at 15.01 Aa, 17.05 Aa, and 17.10 Aa in the RGS spectra. At low turbulent velocities, the gas becomes optically thick in the 15.01 Aa line due to resonant scattering, while the 17 Aa lines remain optically thin. They find that the ... line ratio in NGC 5813 is significantly higher than in NGC 5044. This difference can be explained by a higher level of turbulence in NGC 5044. (ProQuest: ... denotes formulae/symbols omitted.)